# CVE-2026-81925: Concrete CMS reflected XSS in conversation date format

Source: https://junglewise.ai/threats/cve-2026-81925-concrete-cms-reflected-xss-in-conversation-date-format  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-15. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-81925 · Severity: medium · CVSS 6.1 · Published 2026-09-15

Concrete CMS, a popular open-source content management system, contains a reflected cross-site scripting (XSS) vulnerability in its conversation messaging feature. An attacker can inject malicious JavaScript through a crafted date format parameter and trick a user into submitting it, allowing the attacker to steal session cookies, deface the page, or perform actions on behalf of the logged-in user. The vulnerability is particularly easy to exploit because the vulnerable endpoint lacks CSRF protection.

Technologies: [Concrete CMS](https://junglewise.ai/threats/technologies/concrete-cms). Vendors: [Concrete CMS](https://junglewise.ai/threats/vendors/concrete-cms).

## Quick answers

**Is CVE-2026-81925 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-81925 being exploited in the wild.

**How severe is CVE-2026-81925?** Medium severity, with a CVSS score of 6.1, published 15 September 2026.

**Which products and versions are affected?** Concrete CMS before 9.5.3.

**Is there a fix for CVE-2026-81925?** A patch was published on 2026-09-15: Fixed in version 9.5.3 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-81925 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-81925?** Check whether you run Concrete CMS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a reflected XSS flaw in Concrete CMS's conversation message rendering code. The root cause is improper neutralization (insufficient output encoding) of user-supplied custom date format strings when rendering conversation messages. An attacker can craft a malicious POST request containing JavaScript payload in the date format parameter and deliver it to a victim user. The attack requires the victim to be authenticated (PR:L) and to interact with a link or form submission (UI:P), but is aided by the absence of CSRF token validation on the endpoint, enabling cross-origin exploitation. The vulnerability affects versions before 9.5.3, and a patch is available in that version.

## Affected products

- Concrete CMS Concrete CMS before 9.5.3

## Timeline

- 2026-09-15: disclosed: CVE-2026-81925 published
- 2026-09-15: patched: Fixed in version 9.5.3

## References

- [https://github.com/concretecms/concretecms](https://github.com/concretecms/concretecms)
- [https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes](https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes)

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